This invention relates to a wire scribed circuit board product and method of manufacture. Specifically this invention relates to wire scribed circuit boards including shielded conductors.
As electronic components become smaller, and as the switching speeds of the components increase, the requirements on the interconnection circuit boards become increasingly severe and difficult to satisfy. The interconnection pattern becomes increasingly dense because of the smaller and more compact components. As the conductors move closer together to provide a denser pattern, however, the crosstalk and noise increases. Increased signal frequencies and higher switching speeds similarly tend to increase crosstalk and noise. At higher switching speeds and signal frequencies, the signal propagation speed in the transmission medium also becomes increasingly important since, for example, in high speed computer designs 50% of the computer cycle time is consumed in propagation delays.
Coaxial conductors are the preferred transmission medium for high frequency signals, particularly digital signals from high speed switching components. A coaxial conductor includes a central signal conductor surrounded by a dielectric which in turn is surrounded by a conductive shield. The shield surrounding the signal conductor retains all of the signal energy inside the coaxial conductor and isolates the signal conductor from the surrounding environment. The shield prevents radiation of energy from the signal conductor thereby reducing or eliminating electrical interference with other signals in vicinity.
Although coaxial conductors are the preferred interconnection medium, they are not widely used in electrical circuit boards because of the difficulty in incorporating such conductors in circuit boards made using automatic or semi automatic production techniques. In particular, difficulties are encountered in isolating the shield from the signal conductor so as to permit separate connections to other components.
Techniques are known for improving performance using conventional printed circuit boards or discrete wired boards. Generally, a minimum spacing is maintained between signal conductors to maintain crosstalk at tolerable levels. The components are located to minimize the length of the conductor runs and to avoid parallel runs of conductors sensitive to signal coupling. A technique known as striplining is also commonly used where conductive areas which do not carry signals are located above and below the signal conductors to provide partial shielding. These conductive areas are usually in the form of ground planes for power planes and can cover large areas or can be confined to specific areas overlying and/or underlying specific signal conductors.